Knockout of CXCR5 increases the population of immature neural cells and decreases proliferation in the hippocampal dentate gyrus.

Stuart MJ, Corrigan F, Baune BT - J Neuroinflammation (2014)

Bottom Line:
This was accompanied by a decrease in Ki67 staining subgranular zone (P = 0.009).Behavioural correlates included a significant increase in baseline locomotor activity in an open field test (P <0.00018) and a decrease in stress reactivity in that test (P = 0.015).CXCR5 reduces maintenance of immature neural cell populations and enhances proliferation of subgranular zone cells in the hippocampal dentate gyrus, however the mechanism of these effects remains unclear.

Background: The process of neurogenesis in which new neurons are generated by proliferation and differentiation of neural stem/progenitor cells (NSCs/NPCs) has been a topic of intensive recent investigation. Investigations of the factors which regulate this process have recently begun to include immune factors including immune cells and cytokines, however the class of immune proteins designated as chemokines have been relatively neglected. Increasing evidence for novel brain-specific mechanisms of chemokines beyond their classical chemotactic functions has suggested that they may play a role in the regulation of NSC/NPC biology.

Methods: We have investigated the role of the chemokine receptor CXCR5 (ligand is CXCL13) in the activity of these cells through neurobiological and behavioural analysis of CXCR5-deficient mice (CXCR5-/-). These investigations included: immunohistochemistry for the markers Ki67, nestin, doublecortin, and IBA-1, neurosphere assays, and the baseline behavioural tests: open field test and sucrose preference test.

Results: We observed a significant increase in doublecortin and nestin staining in the hippocampal dentate gyrus (P = 0.02 and P = 0.0008, respectively) of CXCR5-/- animals as compared to wild-type controls. This was accompanied by a decrease in Ki67 staining subgranular zone (P = 0.009). Behavioural correlates included a significant increase in baseline locomotor activity in an open field test (P <0.00018) and a decrease in stress reactivity in that test (P = 0.015). Deficiency in CXCR5 was not associated with alterations in hippocampal microglial density, microglial activation or systemic cytokine levels, nor with loss of NSC/NPC populations in the neurosphere assay.

Conclusions: These findings are the first to describe a brain-specific function of CXCR5 under physiological conditions. CXCR5 reduces maintenance of immature neural cell populations and enhances proliferation of subgranular zone cells in the hippocampal dentate gyrus, however the mechanism of these effects remains unclear. Further research into the regulation of NSC/NPC activity should consider investigation of CXCR5 and other chemokines which may be relevant to the pathophysiology of psychiatric disorders including depression, anxiety and cognitive impairment/dementia.

Mentions:
To further interpret the observed in-vivo effects of the CXCR5 deficiency we also analysed the in-vitro activity of several subgroups of NPC/NSCs via the neurosphere culture method. We considered separately the populations of small (≥50 μm) and large (≥250 μm) hippocampus derived neurospheres both under basal culture conditions and the latent populations which are responsive to depolarisation with KCl. Previous studies have described the properties of these populations to include cells of both NPC and in the case of KCl responsive large spheres NSC phenotype[21]. In this study we detected no significant effects of CXCR5 deficiency on any of these hippocampal populations in number or size (n = 10 per group; all P >0.05) (Figure 2). We also detected no significant difference in SVZ derived neurospheres (75.5 ± 12.5 vs. 110.9 ± 15.5; n = 10 per group; P = 0.1) (data not shown). Considered in parallel with the above data, this suggests that the observed reduction in Ki67 staining seen in CXCR5-/- animals is not due to an absolute loss of NPC/NSC populations as these are still reactive to appropriate in-vitro stimulus. This implies that CXCR5 signalling is not required for maintenance of the proliferative capability of latent NPC/NSC populations.

Mentions:
To further interpret the observed in-vivo effects of the CXCR5 deficiency we also analysed the in-vitro activity of several subgroups of NPC/NSCs via the neurosphere culture method. We considered separately the populations of small (≥50 μm) and large (≥250 μm) hippocampus derived neurospheres both under basal culture conditions and the latent populations which are responsive to depolarisation with KCl. Previous studies have described the properties of these populations to include cells of both NPC and in the case of KCl responsive large spheres NSC phenotype[21]. In this study we detected no significant effects of CXCR5 deficiency on any of these hippocampal populations in number or size (n = 10 per group; all P >0.05) (Figure 2). We also detected no significant difference in SVZ derived neurospheres (75.5 ± 12.5 vs. 110.9 ± 15.5; n = 10 per group; P = 0.1) (data not shown). Considered in parallel with the above data, this suggests that the observed reduction in Ki67 staining seen in CXCR5-/- animals is not due to an absolute loss of NPC/NSC populations as these are still reactive to appropriate in-vitro stimulus. This implies that CXCR5 signalling is not required for maintenance of the proliferative capability of latent NPC/NSC populations.

Bottom Line:
This was accompanied by a decrease in Ki67 staining subgranular zone (P = 0.009).Behavioural correlates included a significant increase in baseline locomotor activity in an open field test (P <0.00018) and a decrease in stress reactivity in that test (P = 0.015).CXCR5 reduces maintenance of immature neural cell populations and enhances proliferation of subgranular zone cells in the hippocampal dentate gyrus, however the mechanism of these effects remains unclear.

Background: The process of neurogenesis in which new neurons are generated by proliferation and differentiation of neural stem/progenitor cells (NSCs/NPCs) has been a topic of intensive recent investigation. Investigations of the factors which regulate this process have recently begun to include immune factors including immune cells and cytokines, however the class of immune proteins designated as chemokines have been relatively neglected. Increasing evidence for novel brain-specific mechanisms of chemokines beyond their classical chemotactic functions has suggested that they may play a role in the regulation of NSC/NPC biology.

Methods: We have investigated the role of the chemokine receptor CXCR5 (ligand is CXCL13) in the activity of these cells through neurobiological and behavioural analysis of CXCR5-deficient mice (CXCR5-/-). These investigations included: immunohistochemistry for the markers Ki67, nestin, doublecortin, and IBA-1, neurosphere assays, and the baseline behavioural tests: open field test and sucrose preference test.

Results: We observed a significant increase in doublecortin and nestin staining in the hippocampal dentate gyrus (P = 0.02 and P = 0.0008, respectively) of CXCR5-/- animals as compared to wild-type controls. This was accompanied by a decrease in Ki67 staining subgranular zone (P = 0.009). Behavioural correlates included a significant increase in baseline locomotor activity in an open field test (P <0.00018) and a decrease in stress reactivity in that test (P = 0.015). Deficiency in CXCR5 was not associated with alterations in hippocampal microglial density, microglial activation or systemic cytokine levels, nor with loss of NSC/NPC populations in the neurosphere assay.

Conclusions: These findings are the first to describe a brain-specific function of CXCR5 under physiological conditions. CXCR5 reduces maintenance of immature neural cell populations and enhances proliferation of subgranular zone cells in the hippocampal dentate gyrus, however the mechanism of these effects remains unclear. Further research into the regulation of NSC/NPC activity should consider investigation of CXCR5 and other chemokines which may be relevant to the pathophysiology of psychiatric disorders including depression, anxiety and cognitive impairment/dementia.